Cellulose nanocrystal/PVA nanocomposite membranes for CO₂/CH₄ separation at high pressure

Biogas can be used as an alternative energy source in place of conventional fossil fuels. However, for this to happen, it is necessary to optimize biogas production as well as improve the biogas quality. Crystalline nanocellulose (CNC) has excellent mechanical properties as well as a high moisture uptake ability. These properties make CNC a promising candidate to be used as an additive in polyvinyl alcohol (PVA)-facilitated transport membranes (FTMs). The overall objective of this work is to develop CNC/PVA nanocomposite membranes for enhancing the biogas quality through CO₂ capture. The effects of CNC concentration and the pH of the casting solution are investigated to optimize CO₂/CH₄ separation. Membrane characterization shows that the addition of CNC affects the degree of swelling, crystallinity and thickness of the resulting membranes, while permeation testing showed that the permeance and selectivity for CO₂ increased with the addition of CNC. Membranes produced with 1% CNC and a casting suspension at pH 10 gave the best results under the given set of conditions. The maximum permeance achieved by the formulated nanocomposite membranes was 0.29 m³(STP)/(m²-h-bar), while the selectivity of CO₂ over CH₄ was 43. It was also observed that increasing the feed gas pressure deteriorated the membrane performance.